Current density redistributing anode

ABSTRACT

Non-ferrous metals are electrowon from aqueous electrolytes at high current densities, without independent agitation to overcome concentration polarization at the cathode, by the use of special electrolytic cells including insoluble anodes that control the current density at particular levels of the electrolyte so that greater densities can be employed at the upper levels by virtue of the agitation induced by gases evolved at the anode, while at the lower levels smaller current densities are employed to avoid problems associated with concentration polarization. Current density control can be achieved by using a downwardly tapered anode, an anode having smaller working surfaces at its lower extremities or an anode made of special materials having preselected resistivities or by placing a non-conductive multiperforate diaphragm between the lower portions of the anode and cathode. The stirring action of the gases evolved at the anode can be enhanced by incorporating a controlled amount of a surfactant in the electrolyte.

United States Patent [191 Ettel [451 June 28, 1974 CURRENT DENSITY REDISTRIBUTING ANODE Inventor: Victor Alexander Ettel, Toronto,

Ontario, Canada Assignee: The International Nickel Company,

lnc., New York, NY.

Filed: Aug. 27, 1971 Appl, No.: 175,456

[30] Foreign Application Priority Data Sept fl, 1970 Canada ..0924 0/70 References Cited UNITED STATES PATENTS Bianchi et al. 204/290 F FOREIGN PATENTS OR APPLlCATlONS 429,206 5/1935 Great Britain ..204/51 Primary Examiner-John H. Mack Assistant Examiner-R. L. Andrews 5 7 ABSTRACT Non-ferrous metals are electrowon from aqueous electrolytes at high current densities, without independent agitation to overcome concentration polarization at the cathode, by the use of special electrolytic cells including insoluble anodes that control the current density at particular levels of the electrolyte so that greater densities can beemployed at the upper levels by virtue of the agitation induced by gases evolved at the anode, while at the lower levels smaller current densities are employed to avoid problems associated with concentration polarization. Current density control can be achieved by using a downwardly tapered anode, an anode having smaller working surfaces at its lower extremities or an anode made of special materials having preselected resistivities or by placing a nonconductive multiperforate diaphragm between the lower portions of the anode and cathode. The stirring action of the gases evolved at the anode can be enhanced by incorporating a controlled amount of a surfactant in the electrolyte.

14 Claims, 6 Drawing Figures minimum @914 3,82 1 097 PATENTEMuze m4 SHEET & 0F 3 Ti T1 4.

FYI/EH70? Z070? A. 57764 rmp/vsy S0 41 I X CURRENT DENSITY REDISTRIBUTING ANODE The present invention pertains to electrochemistry, and more particularly to electrowinning and apparatus therefor.

Frequently, metal values, such as copper, are most economically recovered from particular ores, ore concentrates, or other metallurgical intermediates by hydrometallurgical techniques. However, the cost of recovering the dissolved metal values from solution can obviate any savings attributable to the initial hydrometallurgical treatment. If the metal values are cemented out or precipitated from solution as sulfides, oxides or hydroxides, the cemented metal values or other com pounds must be further treated to refine the metal values to a commercially acceptable form and purity. in many instances, the cementation or precipitation reagent costs, when coupled with subsequent processing costs, render the initial hydrometallurgical recovery economically impractical.

Dissolved metal values can also be recovered directly from solution by chemical reduction methods. This process requires that the solution be first concentrated and/or purified before the metal values can be economically recovered. Although this process works reasonably well for copper, the copper product is frequently contaminated with sulfur and other components of the solution, such as nickel and iron. In addition, the conditions of temperature and hydrogen partial pressures require the use of heavy autoclaves which can experience corrosion due to free acid liberated by the reduction reactions.

Electrowinning has also been commercially employed to recover metal values from solution. Electrolytic recovery of metal values is advantageously employed where electrical energy is inexpensive and when the solutions are amenable to electrolysis. Since metal values arerecovered from solution without the addition of further reagents, the electrolyte can be recycled for leaching purposes whereby overall reagent costs are minimized.

As is well understood in the art, electrowinning involves electrodeposition of metal values on a cathode with the electrical circuit being completed by use of an insoluble anode at which oxygen or chlorine is evolved. The rate of electrodeposition is practically limited by a phenomenon often referred to as concentration polarization which manifests itself by the production of roughened cathode deposits that can occlude electrolyte thereby contaminating the cathode. Concentration polarization with concomitant rough deposits becomes more apparent at increasing current densities. At sufficiently high current densities, the potential of the electrowinning cell rapidly rises to a level at which hydrogen is liberated at the cathode. That current density at which hydrogen is liberated at the cathode is known as the limiting cathode current density. Even before reaching the limiting cathode current density, the cathode deposit becomes noticeably rough and striated. Therefore, as a practical matter, there exists a some what arbitrary current density at which the cathode deposit becomes so rough as to be commercially unacceptable and that current density, which is dependent upon a number of factors including electrolyte composition, electrolyte temperature, electrolyte additives, cell geometry and the like, is referred to herein as the cathode current density limit. By way of example,

the cathode current density limit for electrowinning copper is most generally between about 20 percent and 40 percent of the limiting cathode current density, and, as a common rule-of-thumb, about percent. Stated somewhat differently, the cathode current density limit will, in the case of electrowinning copper, be that current density which produces a cathodic overpotential of between about 40 millivolts (mv) and 90 mv above the equilibrium potential for copper.

Since electrolytic cells occupy large spaces, involve large capital expenditures and contain great quantities of materials in process, it is highly desirable to maximize the rates of production without wasting electrical energy. High production rates are realized by employing high current densities because the productivity of an electrowinning cell is a direct function of the current density employed.

The effects of concentration polarization, including low cathode current density limits, can be minimized by increasing the rate of diffusion of metal values to the metal-value-depleted cathode layer. For example, the temperature of an electrolyte can be increased to increase the rate of thermal diffusion. Mechanical stirring or circulation can also be employed to increase mass transport. However, these methods are not always entirely satisfactory because the corrosive nature of the electrolyte imposes severe limitation on the types of material and apparatus that can be employed. F urthermore, independent agitation can stir up and resuspend settled slimes which are then unavoidably incorporated in the cathode deposit. lt has also been suggested that solutions, more concentrated in metal values, would permit the use of higher current densities, but it is frequently difiicult or impractical to provide more concentrated solutions. Although many attempts were made to overcome the foregoing difficulties and other disadvantages, none, as far as I am aware, was entirely successful when carried into practice commercially on an industrial scale.

It has now been discovered that the productivity of electrowinning processes can be increased, without increasing the size or number of cells, employing high temperatures, or concentrated solutions or independent mechanical agitation, by use of specially designed insoluble anodes.

It is an object of the present invention to provide a more efficient electrowinning process.

Another object of the present invention is to provide an electrowinning process employing high current densities.

Yet another object of the present invention is to provide an electrowinning operation in which variable anode current densities are employed to enable the use of higher overall current densities.

Still another object of the present invention is to provide an electrowinning process that effectively employs gas evolved at the anode to facilitate diffusion of metal values in the electrolyte.

A further object of the present invention is to provide a special anode for electrowinning metals from solution.

ning cell for the recovery of metals from solution which cell allows the use of high current densities.

Other objects and advantages will become apparent from the following description taken in conjunction with the accompanying drawing in which:

An even further object is to provide an electrowin- FIG. 1 is a pictorial view of an electrowinning cell in accordance with the invention, partly in section, showing a single anode-cathode combination;

FIG. 2 is a cross-sectional view of FIG. 1 taken along the line 2-2;

FIG. 3 is a pictorial view of another embodiment of an anode in accordance with the present invention;

FIG. 4 is an even further embodiment of an anode in accordance with the present invention;

FIG. 5 is yet another embodiment of an anode in accordance with the present invention; and

FIG. 6 is a cross-sectional view of another electrowinning cell in accordance with the present invention.

Generally speaking, the present invention contemplates an electrowinning method to recover dissolved metal values from an electrolyte. An electrolyte having dissolved therein at least one electrodepositable metal, such as copper, nickel and cobalt is established. An electrolytic cell is established by immersing, in a generally vertical direction, a cathode having a working surface defined by lower and upper region and an insoluble anodein the electrolyte. The metal is electrodeposited in greater amounts on the upper region of the cathode than on the lower region by employing higher cathode current densities at the upper regions than at the lower regions, whereby productivity of the electrolytic cell can be increased by at least about 10 percent.

In electrowinning processes, as distinguished from electrorefining processes, gas, usually oxygen when aqueous electrolytes are employed, is evolved as bub bles at the anode surface. As these bubbles break free from the anode and rise through the electrolyte, the electrolyte is effectively agitated and mass transport is facilitated. The motion of the gas bubbles is such that the induced agitation is effective at both anode and cathode surfaces. Contrary to expectations, the bubbles do not merely rise to and burst at the surface of the electrolyte, but generally circulate upwardly past the anode surface, across the electrolyte to the cathode and downwardly past the cathode surface. Bubbleinduced agitation at both anode and cathode is more vigorous in the shallow regions of the electrolyte, i.e., toward the top of the bath, due to the cumulative effect of all the bubbles produced at the more deeply immersed portions of the anode. The vigorous agitation provided by the bubbles in the more shallow regions of the electrolyte is effective in minimizing concentration polarization at the upper regions of the cathode, but the phenomenon of concentration polarization is encountered at the lower, i.e., more deeply immersed, portions of the cathode. The process in accordance with the present invention takes advantage of the bubble-induced agitation by employing higher cathode current densities at the upper regions of the cathode where such agitation is highly effective and by employing lower cathode current densities at the lower cathode regions where bubble-induced agitation is less effective or even minimal.

Localized current densities between the anode and cathode can be controlled by various techniques. In effect, the total resistance of the current path measured from the top of the anode to a particular vertical point on the anode thence horizontally through the electrolyte to a corresponding vertical point on the cathode increases from the top to the bottom of the anode. The increase in the total resistance is controlled to be sufficiently great so that the practical cathode current density limit is not exceeded at any depth. The differential increase in total resistance, i.e., the difference in total resistance at different electrolyte levels, can be obtained by using anode materials that have resistivities greater than heretofore thought practical, by controlling the cross-sectional shape of conventionally employed anodes and cathodes, by adjusting the conductive surface areas of conventional anodes, by employing an anode that has increasing resistivities from top to bottom, by controlling the positioning of anodes in the electrolytic cell or by combinations of any of the foregoing.

Referring now to the drawings, which are merely for the purpose of showing advantageous embodiments of the present invention and not for limiting same. FIGS. 1 and 2 show an electrowinning cell 10 equipped with an anode in accordance with the present invention. Electrolytic cell 10 includes a tank 12 which is advantageously made of concrete and is lined with rubber or other suitable inert material 14. Tank 12 is provided with bus bars 16 and 18 through which electric current, from a source not shown on the drawings, is applied to anode 20 and cathode 22 via contact bars 24 and 26, respectively, and cathode straps 28. Electrolyte 30 is continually pumped into and out of electrolytic tank 12 by means not shown on the drawing as the electrolyte is depleted in metal values by electrodeposition on cathode 22.

As is well known in the art, electrolytic cells are most frequently connected in series with each cell containing one additional anode so that alternately placed anodes and cathodes are bounded by an anode at each end. Se-

ries arrangement of electrolytic cells is effected by placing tanks side by side so that, for example, current flowing through bus bar 16 is conducted through anode contact bar 24 and anode 20 through electrolyte 30 to cathode 22 and through cathode strap 28, contact bar 26 and bus bar 28 to anode contact bar 32 for the immediately adjacent electrolytic cell, not shown on the drawings. Contact bars 24 and 26 are supported at opposite ends by nonconducting supports 34 and 36, respectively, to insure that the electrodes are in a level position and to ensure the desired circuit for the current. I

Anode 20 depicted in FIGS. 1 and 2 has a form that is advantageous for the practice of the present invention. Although the present invention is not limited to any particular anode dimensions or specific anode shapes, a typical example, given solely for the purpose of illustrating the invention, is an anode having an overall submerged length of 36 inches and is proportioned so that the upper third, 0, of the anode has a thickness of 1.2 inches and the lower third, 0, has a thickness of 0.3 inch while the middle third, b, is tapered from 1.2 inches at its top to 0.3 inch at its lower portion. It should be noted that the anode depicted in FIG. 2 has a solid cross-section, but the shaped anode can be hol low with appropriate interior supports to minimize warping of the working surfaces. Assuming that the anode and cathode are spaced center to center at about 2.0 inches, and that the cathode is 0.5 inch thick, and that the evolved gas does not change the resistivity of the electrolyte at different depths, the resistivity due solely to the shaped anode and the increased distance between the anode and cathode at the deepest depths is 1.4 times more for the lower third of the anode than for the upper third of the anode. Of course, the rising bubbles, by displacing the conductive electrolyte with nonconducting gas, increase the resistivity of the electrolyte more at shallow depth, because of the greater number of bubbles present in the upper strata of the electrolyte. The increase of resistance due to the greater amount of electrolyte between the lower third of the anode and cathode effectively provides lower current densities for the lower third portion of the electrolytic cell. At the anode, gas, such as oxygen, is evolved and effectively agitates the upper portions of the electrolyte so that higher current densities can be employed. The shaped anode takes advantage of the agitation provided by the evolved gases by insuring that higher current densities are employed at those areas where agitation is more effective in replenishing metal values in the layer of electrolyte immediately adjacent the cathode face. Thus, by employing varying current densities, which varying current densities approach the cathode current density limit at each level, higher overall average current densities can be employed thereby increasing the productivity of the cell.

Anode can be made of any insoluble material. Advantageously, from the viewpoint of overall cost, anode 20 is made of lead or lead-base materials. For example, a lead-base alloy containing 6 percent antimony, for the purpose of strengthening the alloy, has been found to have the requisite properties of strength and insolubility for use as an anode in accordnce with the present invention. Other materials which can be employed to form the shaped insoluble anodes in accordance with the present invention include copper-silicon alloys, magnetite and alloy cast irons. Shaped anodes in accordance with the present invention can be formed by well-known means such as by casting or rolling.

Cathode 22 is primarily a rigid, flat sheet of a metal such as copper, titanium or stainless steel and should be sufficiently heavy that it will hold a steady position within the electrowinning cell. Straps 28 are tacked on the cathode sheet 22 to form a loop to fit over contact bar 26. Of course, any other well known type of cathode can be employed as long as it will hold steady in the electrolytic cell.

Another embodiment of the shaped anode in accordance with the present invention is illustrated in FIG. 3. Anode 40 comprises a sheet 42 made of a material described hereinbefore and provided with a contact bar 44. The third lowermost portion d of cathode 40 is provided with a series of spaced circular holes 46 to lower the surface area of that portion of the anode. Holes 46, by limiting current flow, effectively increase the path of electrical current from the edges of holes 46 to a point diametrically opposed to the center of holes 46 on the cathode. The increased distance between the edges of holes 46 and the cathode increases the IR drop through the solution thereby effectively lowering the current density for the lowermost one-third portion of the cathode. Although this embodiment works reasonably well, it is to be noted that anode 42 in the vicinity of holes 46 experiences comparatively fast corrosion due to current concentrations at these edges. Such corrosion is not desirable since the products of corrosion can contaminate the finished cathode product. Also, the anodes must be frequently replaced thereby increasing overall costs of the operation.

An even further embodiment of the shaped anode in accordance with the present invention is illustrated in FIG. 4. Anode 50 comprises a sheet 52 made of the same material described hereinbefore. Anode 50 is also provided with contact bar 54 made of a conductive material such as copper. The third lowermost portion e of anode 50 is masked at spaced intervals with electrically insulating strips 56. Insulating strips 56 act in much the same manner as holes 46 in anode 40, depicted in FIG. 3. Masking provides an effective means of decreasing the working area of the anode to effectively decrease the current density at the lowermost portions of the cathode. Although the masked anodes are not subjected to rapid deterioration by corrosion as experienced by the anodes depicted in FIG. 3, the masking should be inspected and repaired when necessary. It might be pointed out that the vertical cross-section of both the anodes illustrated in FIGS. 3 and 4 is generally rectangular in shape since holes 46 in FIG. 3 and masking 56 in FIG. 4 eliminate the need for varying the cross-section of the anodes described in FIGS. 3 and 4 in addition to reducing the weight of the anode, and simplifying the manufacture of the anode sheets 42 and 52, respectively.

As noted hereinbefore, decreasing the current density for the lowermost portions of the anode can be accomplished by the use of particular materials in the anode. This embodiment of the invention is depicted in FIG. 5 wherein anode 60 comprises a sheet 62 of expanded titanium mesh. Sheet 62 is mounted on contact bar 64 to provide good electrical conduction therebetween. In order to stifien sheet 62 and to distribute current, the anode is provided with titanium support bars 66. It is well known that titanium is anodically oxidized in acidic electrolytes producing a highly passive and electrically resistive oxide layer which only breaks down at potentials in excess of 20 volts, at which potential metallic titanium dissolves in the electrolyte. Therefore, it is advantageous to coat the titanium mesh sheet 62 with a noble metal such as platinum. The thickness of the noble metal coating is maintained as thin as possible to lower capital expenditures while being of sufficient thickness to minimize oxidation of the titanium mesh and to provide electrically conductive surfaces. Titanium support bars 66 need not be coated with a noble metal since their function is to strengthen the sheet 62 and to distribute current, and once strips 66 are fastened to sheet 62 electrical contact is insured and such electrical contact is not destroyed by oxygen evolved at the anode.

Another embodiment of the present invention is depicted in FIG. 6. Electrowinning cell 70 comprises a suitable tank 72 that holds electrolyte 74, vertically disposed cathode 76 that is connected to a current source by contact bar 78, anode 80 (that can be optionally slightly tapered as shown in F IG. 6 but not to the extent shown in FIG. 2) that is connected to a current source by contact bar 82 and multiperforate diaphragm 84 that can be made of suitable non-conducting material, such as polyethylene or polyvinyl chloride; Multiperforate diaphragm 84 effectively lowers the current density at cathode 76 by restricting the flow of current through the electrolyte. This embodiment is particularly advantageous in that, although it is similar to masking the anode, the problems associated with masking materials being torn from the anode are avoided.

An advantageous embodiment of the present invention is to incorporate a surface active reagent (a surfactant) in the electrolyte to enhance the stirring action of the gases released at the anode. The surfactant can be added in amounts up to about 500 parts per million (ppm) or even larger amounts although no added benefits are realized when more than 500 ppm are employed and any benefits gained are offset by the added cost of oxidation losses of the surfactant. Enhanced stirring, as evidenced by a smoother cathode deposit, is observed at surfactant additions as low as about 1 ppm, but at such low concentrations full enhancement of stirring by released gases at the anode is not obtained and losses of the surfactant by oxidation or volatilization rapidly diminish any benefits gained by the use of a surfactant. In most instances, the surfactant is added to the electrolyte in amounts between about ppm and 50 ppm. Any surfactant that is chemically and physically stable at electrowinning conditions and that is soluble in the electrolyte can be employed. Examples of surfactants that can be employed are the sodium salt of dodecylated oxydibenzene disulfonate, dodecylated oxydibenzene disulfonic acid, sodium N-alkyl-carboxy sulfosuccinate, and sodium alkylsulfosuccinate.

For the purpose of giving those skilled in the art a better understanding of the invention, the following illustrative examples are given:

EXAMPLE I A shaped anode 32 inches wide and 43 inches long with the cross section as described in conjunction with FIGS. 1 and 2 was cast from a lead-base alloy containing 6 percent antimony. The anode was immersed in electrolyte containing 60 grams per liter of copper, 4 grams per liter (gpl) of nickel, l gpl of cobalt, 5 gpl of iron, 1 gpl of arsenic, 20 ppm dodecylated oxydibenzene disulfonate acid and 145 gpl of free sulfuric acid and at a distance, center to center, of 2 inches from a copper starting sheet.

The cell was operated at an average cathodic current density of 31 amps per square foot at a cell voltage of 2.0 volts. The local current densities for the top third of the cathode were 36 amps per square foot and 26 amps per square foot for the lower third. The cathode plate was very smooth and free of nodules and deep striations.

For comparative purposes a reference run under similar conditions, including the same average current density, electrolyte and temperature, but with a conventional anode, which was a one-half inch thick sheet of a lead-base alloy containing 6 percent antimony and 32 inches wide by 43 inches deep, was made and a cathode having deep striations, general roughness and nodulation was observed at the bottom third of the copper cathode. With a conventional anode the maximum cathodic current density that can be employed while insuring an acceptable cathode is 26 amps per square foot. Thus, by employing an anode in accordance with the present invention .the productivity of a conventional electrolytic cell can be increased by about 20 percent without employing independent agitation, higher temperatures or increased concentrations.

EXAMPLE II An anode as depicted in FIG. 3 was made from a onefourth inch thick sheet of a lead alloy containing 6 percent antimony. The sheet was 32 inches wide and 43 inches deep and was mounted on a copper contact bar. The bottom third of the sheet was provided with a se ries of staggered holes 2 inches in diameter and spaced 3 inches center from center thereby reducing the area of the lower, third of the anode by approximately 34 percent. This anode along with a starting sheet was immersed in a copper sulfate electrolyte of the same composition and at the same temperature as described in Example I to form an electrolytic cell.

The cell was operated at an average cathodic current density of 28 amps per square foot at a cell voltage of 2.15 volts. The local cathode current densities were 30 amps per square foot for the upper part of the cathode, and 26 amps per square foot for the bottom.

The thickness of the cathodic copper plate was approximately proportional to the local cathode current densities, and the plate was substantially smooth and free of nodules and deep striations even at the bottom third.

EXAMPLE Ill An anode as described in FIG. 5 is manufactured from a 32 inch wideby 43 inch deep sheet of 1.5 times 0.5 inch expanded titanium mesh, provided with four reinforcing and current distributing titanium strips running from the contact bar down to the bottom end of the anode, so that the anode structure had an electrical resistance of 6.1 X 10 ohms from the contact bar to the bottom end. The anode, except for the current conducting strips, was plated with a one micron coating of platinum. The anode was used in a conventional electrowinning cell with a copper sulfate electrolyte of the same composition and the same temperature as de scribed in Example I.

The electrolyte was maintained at a temperature of 50C., and an average cathodic current density of 28 amps per square foot at a cell voltage of 2.2 volts was impressed upon an anode and cathode immersed in the electrolyte. The local cathodic current density values decreased gradually from 32 amps per square foot at the top of the cathode to 25 amps per square foot at the bottom. The cathode copper plate thickness increased approximately at the same ratio as the local current densities, and the cathode was substantially smooth and uniform, even on the bottom part, where, under the same conditions, considerable roughness and nodular growth was observed with a conventional anode. With a conventional anode an average current density of 25 amps per square foot would have been employed since it is at this value that the effects of concentration polarization would be first observed at the bottom of the cathode in the absence of any independently supplied agitation. Thus, by employing an anode in accordance with the present invention, the productivity of an electrolytic cell containing a titanium mesh anode could be increased by 14 percent without supplying independent agitation or increasing the temperature or concentration of the solution.

It will be observed that the present invention provides an improved insoluble anode that comprises means for controlling the current flowing from the anode to the cathode to provide decreasing cathode current densities for increasing immersion depths so that the cathode current density limit is not exceeded at any given depth.

It will also be observed that the present invention provides an improved electrowinning cell which comprises a tank; a non-ferrous-metal-containing electrolyte held with the tank; at least one cathode substantially vertically immersed in the electrolyte; at least one insoluble anode substantially vertically immersed in the electrolyte and spaced from the cathode; a direct cur rent source for supplying electric current to the anode and cathode to electrodeposit the non-ferrous metal on the cathode and means for controlling the current flowing from the anode to the cathode to provide decreasing cathode current densities for increasing immersion depths so that the cathode current density limit is not exceeded at any given depth.

Although the present invention has been described in conjunction with preferred embodiments, it is to be understood that modifications and variations may be resorted to without departing from the spirit and scope of the invention, as those skilled in the art will readily understand. Such modifications and variations are considered to be within the purview and scope of the invention and appended claims.

I claim:

I. A method for electrowinning copper, nickel, and cobalt metal values which comprises: establishing a bath of an electrolyte having dissolved therein at least one electrodepositable metal; immersing a cathode and an insoluble anode in the electrolyte in a generally vertical direction to form an electrolytic cell, the cathode having a working surface defined by upper and lower regions; and electrodepositing greater amounts of the metal on the upper region of the cathode than on the lower region by employing higher cathode current densities at the upper regions than at the lower regions whereby productivity of the electrolytic cell is increased by at least about 10 percent and thick, smooth electrodeposits are produced.

2. A method for electrowinning copper from solution which comprises: establishing a bath of an electrolyte having copper dissolved therein; establishing an electrowinning cell by immersing in the electrolyte an insoluble anode and a substantially vertically disposed cathode, upon which dissolved metal values are electrodeposited, to provide a pair of spaced and opposed anode and cathode working surfaces, the working surfaces having corresponding opposed upper and lower regions; increasing the electrical resistance of the current path from the upper anode region through the anode and the electrolyte to the cathode with increasing electrolyte depth so that lower current densities between the corresponding regions are produced for increasing electrolyte depths; and passing electrical current between the anode and cathode via the electrolyte to establish an average current density, to electrodeposit copper on the cathode and to evolve gas at the anode, which evolved gas provides increasingly efficient agitation of the electrolyte so that a vertical cathode current density limit differential is established whereby the current density between the anode and cathode at any particular depth is controlled so that it approaches but does not exceed the cathode current density limit for smooth plating at that depth to thereby provide an overall higher average current density whereby productivity of the electrolytic cell is increased by at least 10 percent, and thick, smooth electrodeposits are produced.

3. The method as described in claim 2 wherein the electrolyte contains a surfactant in small but effective amounts to increase the stirring action of gases released at the anode.

4. The method as described in claim 2 wherein the electrolyte contains a surfactant in an amount of at least about one part per million per liter.

5. The method as described in claim 2 wherein the 5 electrolyte contains a surfactant in an amount up to about 500 parts per million per liter.

6. The method as described in claim 2 wherein the electrolyte contains a surfactant in an amount between about parts per million per liter and 50 parts per million per liter.

7. The method as described in claim 2 wherein the electrolyte contains a surfactant selected from the group consisting of the sodium salt of dodecylated oxydibenzene disulfonate, dodecylated oxydibenzene disulfonic acid, sodium N-alkylcarboxy sulfosuccinate and sodium alkylsulfosuccinate.

8. A method for electrowinning copper from solution which comprises: establishing an electrowinning cell by vertically immersing a cathode, upon which copper is deposited, and an insoluble anode into an electrolyte that contains copper; and passing an electric current between the cathode and anode via the electrolyte to establish an average current density, to electrodeposit copper on the cathode and to evolve gas at the anode which gas provides increasingly efficient agitation of the electrolyte from deeper to less deep portions of the electrolyte, so that a vertical cathode current density limit differential is established with the current density between the anode and cathode at any particular depth being controlled so that it approaches but does not exceed the cathode current density limit for smooth plating at that depth whereby overall higher average current densities can be employed whereby productivity of the electrolytic cell is increased by a least 10 percent, and thick, smooth electrodeposits are produced.

9. An insoluble anode that is substantially verticaly immersed in a non-ferrous-metal-containing electrolyte for electrowinning the non-ferrous metal from the electrolyte by electrodeposition on a substantially vertically immersed cathode, comprising an anode having holes in its lower portions which holes decrease the surface area of the lower portions of the anode to effectively decrease cathode current densities at the more deeply immersed portions of the cathode.

10. An insoluble anode that is substantially vertically immersed in a non-ferrous-metal-containing electrolyte for electrowinning the non-ferrous metal from the electrolyte by electrodeposition on a substantially vertically immersed cathode, comprising an anode having controlled parts of its lower portion masked with an electrically insulating material to decrease the surface area of the lower portions of the anode to effectively decrease cathode current densities at the more deeply immersed portions of the cathode.

ll. An insoluble anode that is substantially vertically immersed in a non-ferrous-metalcontaining electrolyte for electrowinning the non-ferrous metal from the electrolyte by electrodeposition on a substantially vertically immersed cathode, comprising an anode and a multiperforate, electrically non-conductive diaphragm surrounding the lower portions of the anode to effectively decrease the cathode current densities at the levels of the diaphragm.

12. An electrowinning cell which comprises a tank; a non-ferrous-metal-containing electrolyte held within the tank; at least one cathode substantially vertically immersed in the electrolyte; at least one insoluble anode substantially vertically immersed in the electrolyte and spaced from the cathode; and a direct current source for supplying electric current to the anode and cathode to electrodeposit the non-ferrous metal on the cathode, said anode having holes in its lower portions which holes decrease the surface area of the lower portions of the anode to effectively decrease cathode current densities at the more deeply immersed portions of the cathode.

13. An electrowinning cell which comprises a tank; a non-ferrous-metal-containing electrolyte held within the tank, at least one cathode substantially vertically immersed in the electrolyte; at least one insoluble anode substantially vertically immersed in the electrolyte and spaced from the cathode; and a direct current source for supplying electric current to the anode and cathode to electrodeposit the non-ferrous metal on the cathode, said anode having controlled parts of its lower 12 portion masked with an electrically insulating material to decrease the surface area of the lower portions of the anode to effectively decrease cathode current densities at the more deeply immersed portions of the cathode.

lyte and spaced from the cathode and a multiperforate, I

electrically non-conductive diaphragm surrounding the lower portions of the anode to effectively decrease the cathode current densities at the levels of the diaphragm; and a direct current source for supplying electric current to the anode and cathode to electrodeposit the non-ferrous metal on the cathode.

Po-ww Umr STATES m rte CERTEKQTE @F QQREQE Patent; No. L821 m7 Dated June 28, 1974 Inventofla) Victor Alexander Ettel It is certified that error appears in the above identified patent and that said Letters Patent are hereby corrected as eho below:

Col. 3, line 22, for "region" read -regions-.-.

Col. 4, line 16, after "same" delete the period and insert a comma Col. 5, line 29, for "accordnce" read accordance.

Col. 9, line 4 of claim 1, for "electrodepositable metal" read -of said metal-.

Rewrite claims 9 through 14 as follows:

9. An insoluble anode that is substantially vertically immersed in a non-ferrous-inetal-containing electrolyte for electrowinning the non-ferrous metal from the electrolyte by electrodeposition on a substantially vertically immersed cathode, comprising an anode having holes only in its lower portions which holes decrease the surface area of the lower portions of the anode to provide decreasing cathode ,current densities for increasing immersion depths so that the cathode current density limit is not exceeded at any given depth.

10. An insoluble anode that is substantially vertically immersed in a non-ferrous-metal-containing electrolyte for electrowinning the non-ferrous metal from the electrolyte by electrodeposition on a substantially vertically immersed cathode, comprising an anode having controlled parts of its lower portion masked with an electrically insulating material to decrease the surface area of the lower portions of the anode to provide decreasing cathode current densities for increasing immersion depths so that the cathode current density limit is not exceeded at any given depth.

ll. An insoluble anode that is substantially vertically immersed in a non-ferrousm etalcontaining electrolyte for electrowinning the non-ferrous metal from the electrolyte by electrodeposition on a substantially vertically immersed cathode, comprising an anode and a multiperforate, electrically non-conductive diaphragm surrounding the lower portions of the anode to provide decreasing cathode current densities for increasing immersion depths so that the cathode current density limit L is not exceeded at any given depth.

P0405" UNITED STATES PATENT @FFEQE (5/69) CERTIEIMA'EE @F QQRREQ'UQN Patent No. 3,821,097 Dated June Q8, 1974 Inventofla) Victor Alexander Ettel It is certified that error appears in the above identified patent and that said Letters Patent are hereby corrected as shown below:

r" Page 2 12. An electrowinning cell which comprises a tank; a non-ferrousmetal-containing electrolyte held within the tank; at least one cathode substantially vertically immersed in the electrolyte; at least one insoluble anode substantially vertically immersed in the electrolyte and spaced from the cathode; and a direct current source for supplying electric current to the anode and cathode to electrodeposit the non-ferrous metal on the cathode, said anode having holes only in its lower portions, which holes decrease the surface area of the lower portions of the anode to provide decreasing cathode current densities for increasing immersion depths so that the cathode current density limit is not exceeded at any given depth.

13. An electrowinning cell which comprises a tank; a non-ferrousmetal-containing electrolyte held within the tank, at least one cathode substantially vertically immersed in the electrolyte; at least one insoluble anode substantially vertically immersed in the electrolyte and spaced from the cathode; and a direct current source For supplying electric current to the anode and cathode to electrodeposit the non-ferrous metal on the cathode, said anode having controlled parts of its lower portion masked with an electrically insulating material to decrease the surface area of the lower portions of the anode to provide decreasing cathode current densities for increasing immersion depths so that the cathode current density limit is'not exceeded at any given depth.

14. An electrowinning cell which comprises a tank; a non-ferrousmetal-containing electrolyte held within the tank; at least one cathode substantially vertically immersed in the electrolyte; at least one insoluble anode substantially vertically immersed in the electrolyte and spaced from the' cathode and a multiperforate, electrically non-conductive diaphragm surrounding the lower portions of the anode to provide decreasing cathode current densities for increasing immersion depths so that the cathode current density limit is not exceeded at any given depth; and a direct current source for supplying electric current to the anode and cathode to electrodeposit the non-ferrous metal on the cathode.

- Signed and sealed this 12th day of November 1974.

(SEAL) Attest McCOY M. GIBSON JR. c. MARSHALL DANN Attesting Officer Commissioner of Patents 

2. A method for electrowinning copper from solution which comprises: establishing a bath of an electrolyte having copper dissolved therein; establishing an electrowinning cell by immersing in the electrolyte an insoluble anode and a substantially vertically disposed cathode, upon which dissolved metal values are electrodeposited, to provide a pair of spaced and opposed anode and cathode working surfaces, the working surfaces having corresponding opposed upper and lower regions; increasing the electrical resistance of the current path from the upper anode region through the anode and the electrolyte to the cathode with increasing electrolyte depth so that lower current densities between the corresponding regions are Produced for increasing electrolyte depths; and passing electrical current between the anode and cathode via the electrolyte to establish an average current density, to electrodeposit copper on the cathode and to evolve gas at the anode, which evolved gas provides increasingly efficient agitation of the electrolyte so that a vertical cathode current density limit differential is established whereby the current density between the anode and cathode at any particular depth is controlled so that it approaches but does not exceed the cathode current density limit for smooth plating at that depth to thereby provide an overall higher average current density whereby productivity of the electrolytic cell is increased by at least 10 percent, and thick, smooth electrodeposits are produced.
 3. The method as described in claim 2 wherein the electrolyte contains a surfactant in small but effective amounts to increase the stirring action of gases released at the anode.
 4. The method as described in claim 2 wherein the electrolyte contains a surfactant in an amount of at least about one part per million per liter.
 5. The method as described in claim 2 wherein the electrolyte contains a surfactant in an amount up to about 500 parts per million per liter.
 6. The method as described in claim 2 wherein the electrolyte contains a surfactant in an amount between about 10 parts per million per liter and 50 parts per million per liter.
 7. The method as described in claim 2 wherein the electrolyte contains a surfactant selected from the group consisting of the sodium salt of dodecylated oxydibenzene disulfonate, dodecylated oxydibenzene disulfonic acid, sodium N-alkylcarboxy sulfosuccinate and sodium alkylsulfosuccinate.
 8. A method for electrowinning copper from solution which comprises: establishing an electrowinning cell by vertically immersing a cathode, upon which copper is deposited, and an insoluble anode into an electrolyte that contains copper; and passing an electric current between the cathode and anode via the electrolyte to establish an average current density, to electrodeposit copper on the cathode and to evolve gas at the anode which gas provides increasingly efficient agitation of the electrolyte from deeper to less deep portions of the electrolyte, so that a vertical cathode current density limit differential is established with the current density between the anode and cathode at any particular depth being controlled so that it approaches but does not exceed the cathode current density limit for smooth plating at that depth whereby overall higher average current densities can be employed whereby productivity of the electrolytic cell is increased by a least 10 percent, and thick, smooth electrodeposits are produced.
 9. An insoluble anode that is substantially verticaly immersed in a non-ferrous-metal-containing electrolyte for electrowinning the non-ferrous metal from the electrolyte by electrodeposition on a substantially vertically immersed cathode, comprising an anode having holes in its lower portions which holes decrease the surface area of the lower portions of the anode to effectively decrease cathode current densities at the more deeply immersed portions of the cathode.
 10. An insoluble anode that is substantially vertically immersed in a non-ferrous-metal-containing electrolyte for electrowinning the non-ferrous metal from the electrolyte by electrodeposition on a substantially vertically immersed cathode, comprising an anode having controlled parts of its lower portion masked with an electrically insulating material to decrease the surface area of the lower portions of the anode to effectively decrease cathode current densities at the more deeply immersed portions of the cathode.
 11. An insoluble anode that is substantially vertically immersed in a non-ferrous-metal-containing electrolyte for electrowinning the non-ferrous metal from the electrolyte by electrodeposition on a substantially vertically immersed catHode, comprising an anode and a multiperforate, electrically non-conductive diaphragm surrounding the lower portions of the anode to effectively decrease the cathode current densities at the levels of the diaphragm.
 12. An electrowinning cell which comprises a tank; a non-ferrous-metal-containing electrolyte held within the tank; at least one cathode substantially vertically immersed in the electrolyte; at least one insoluble anode substantially vertically immersed in the electrolyte and spaced from the cathode; and a direct current source for supplying electric current to the anode and cathode to electrodeposit the non-ferrous metal on the cathode, said anode having holes in its lower portions which holes decrease the surface area of the lower portions of the anode to effectively decrease cathode current densities at the more deeply immersed portions of the cathode.
 13. An electrowinning cell which comprises a tank; a non-ferrous-metal-containing electrolyte held within the tank, at least one cathode substantially vertically immersed in the electrolyte; at least one insoluble anode substantially vertically immersed in the electrolyte and spaced from the cathode; and a direct current source for supplying electric current to the anode and cathode to electrodeposit the non-ferrous metal on the cathode, said anode having controlled parts of its lower portion masked with an electrically insulating material to decrease the surface area of the lower portions of the anode to effectively decrease cathode current densities at the more deeply immersed portions of the cathode.
 14. An electrowinning cell which comprises a tank; a non-ferrous-metal-containing electrolyte held within the tank; at least one cathode substantially vertically immersed in the electrolyte; at least one insoluble anode substantially vertically immersed in the electrolyte and spaced from the cathode and a multiperforate, electrically non-conductive diaphragm surrounding the lower portions of the anode to effectively decrease the cathode current densities at the levels of the diaphragm; and a direct current source for supplying electric current to the anode and cathode to electrodeposit the non-ferrous metal on the cathode. 